The PHILCO Phorum

its taken a while but i am getting close to the end.after finding several wiring errors that were corrected it finally plays music but only on a 640kc station,im no radio expert by any means but it appears to be in the oscillator somewhere.i read all the coils during the rebuild all measured ok.its been recapped and all the resistors are modern it plays quite loudly if turned all the way up.its currently hooked up to the concertina wire atop my wall for a antenna.ive rechecked the oscillator wiring and i dont see any errors.ive swapped the 77 tubes but it made no difference.the variable tuning cap i cleaned in dish washing soap brushing as much that was possible.i deoxited the shaft wipers and lubed them and the bearings and cleaned all the trimmer caps to include those on the tuning cap. the hardest part was trying not to get lost as the color coding on the wires disappeared decades ago and yes it has a 'GIMMICK'. i'm new at this and am visiting from audio karma.any and all recommendations are appreciated.

What are you using for a VOM to make both voltage and resistance measurements?

Some digital meters DVM's can tell lies when measuring the resistance of an inductor and capacitance of a "leaky" capacitor.

Use an analog VOM to make B+ measurements as compared to published values for the radio.

Some models of Philco radios have RF, oscillator coil problems. In between layers of windings a celluloid insulating liner was used. The celluloid decomposes and etches into the copper via cracks in the enamel. The oxides and cause leakage winding to winding.

Poor mechanical connections to the chassis can also be a problem. No ohmmeter can detect the issue, so advice is to solder to chassis or drill out rivet and replace with new hardware.

Why were there wrong connections? Was this a radio hacked by another?

I see this radio has been an on-going project.

Take some very sharp pictures of the under chassis, often there is a clue to what is going on that a picture would help.

Oscillator failure can be diagnosed by using a portable radio and searching for the oscillators signal. Re-tuning the the test radio up and down the band to verify the oscillator does not "drop out".

Chas

i use a fluke 79,but do have a simpson 260 on hand. it didnt originate here it was a gift from a friend who was visiting from wa. state.HACKED doesnt do it justice and god only knows if it ever worked when its last repair was done. i rebuilt all the bakelite blocks as per the phlilco repair bench. it took a while to get a filter cap can to stuff with new 10 mfd film caps.i wish i had a WIRING DIAGRAM with all the color codes as i would have been able to more easily able to check the point to point wiring.i would have re-wired the whole thing. the ground path seems intact.lastly the far right compensator cap doesnt seem to have any effect

The Fluke should be O.K. for the measurements but keep the 260 handy for "sanity" checks.

Old Timers advice, "Any adjustment that doesn't work is broken" Meaning there is an associated coil that is tuned by the trimmer, that coil is probably open or there is a poor connection, somewhere...

If you have dud tubes of the same pin configuration laying about, take some very coarse sandpaper to the pins and sand them well. That makes the pins very rough. When the dud tube is plugged in repeatedly, the roughness will clean oxidation from the very sides of the tube socket contacts where it counts.

Most of the antenna coil oscillator and IF coil resistance will be very low, most not over 30 ohms. If the resistances are up, that coil is suspect of being open.

The 260 can be used to do leakage between the windings in the high ohms settings. There should be zero leakage. Any leak between windings is a defective coil.

Most of Philco coils from this era can be rewound, it is a project to get it right...

I suspect the radio has some underlying fault that caused a previous mechanic to run amuck. That fault will be hard to find, remember to suspect any mechanical connection. After all these years the cadmium or zinc plating gets oxidized even on parts in intimate contact. It is those connections that get overlooked.

The 260 set to low ohms may reveal a bad mechanical joint as it is passing current through that the Fluke may not.

Begin with a look at the unresponsive trimmer.

Then get all the voltage readings looking for errors, correct them.

Re-align the set and see where it is at. Follow the advice in my first post...

Still "dead" then some means to inject signal is needed.

However, this is a three tube radio and only two tubes are actually "radio" the third is an audio amp...  

GL!

Chas

[attachment=19822]

as i search for a "d" cell for the simpson i read all the 77 tube voltages.with 118 vac at the the plug p-k  (2-5) on the osc.was 245 vdc and 100vdc on sg-k (3-5) while the 2nd 77 p-k had 50 vdc 20 volts low.and sg-k (3-5) was 29 vdc. as far as correcting the 20v low after checking the resistors i cant find any fault and none run real hot.i can only assume that the tube is dragging it low. so few parts and so hard to find. i dont suppose that ancient .0014 mica cap is suspect even tho i know mica caps last forever.

i had previously wire brushed the pin sockets and deoxited them but i've no way to test the tubes save for the heaters.they all get warm and glow is all i can say.yesterday i removed and ohmed out the antenna and oscillator coils.they looked fabulous and was tempted to polyurethane coat them but decided against it. they were dirty and no outward signs of corrosion cleaned them in alcohol and a final rinse of non residue contact cleaner.the fluke readings were slightly different than the 260 readings but nothing significant. the ground tab on the oscillator was flaky so i put in a bonding wire using a ring stud terminal under the screw. fired it up again but no change. for the helluvit it replaced the .0014 mica with a .001 silver mica and no change.very strange these tube radio's wire going to the cap on the 2nd detector makes it squeal if i squeezie it while the set is on. i guess i become a capacitor to ground! looking for a cheap portable radio fot testing

it would appear that as i couldnt get a squeal using the 2nd radio oscillator test that the oscillator stage is inoperative